Speaking of Precision

Another fascinating article on steel, Milo. Bravo.

It's been my experience that cold working of steel causes some self heating of the steel. How critical of an effect, if any, does this self heating play in making this work a plastic deformation instead of an elastic deformation?

I don't know if that can be answered easily and simply in a reply or if this is potentially grist for another full article. If I maybe so bold, I'd like to add another potentially deep question.

I suspect that elastic deformation has little to do with metal fatigue, how does plastic deformation play into metal fatigue?

You are a keen observer about the self heating, Redfred. Just bending a coat hanger wire back and forth a couple of times will make it quite hot to the touch. We got into the high 200's/ low 300's on cold drawing using an handheld infrared thermometer. I'll queue up your questions for future blogs. Thank you for the feedback. Milo

Several things here. The slip plane diagram. My teacher had a box, more of a tray than a box, with a lot of marbles in it. He used it to demonstrate the softness of annealed iron, how it could be work hardened by disrupting the shear planes, and by the insertion of different size atoms or molecules, which, just by being there also disrupted the planes.

Another reaction was to wonder if a non-plastic material would melt. It probably would, as ice suddenly becomes water, but we would miss the softening when we warm up the metal.

I once designed the hoppers for holding iron dust for an explosive casting system (is that the right description? I guess that there is enough heat generated by the intense pressure that it melts the dust sufficiently to fuse it but not melt it, thinking that if it was melted it would not hold shape. The blacksmith creates a lot of heat in the metal from his hammer in as well as the forge.

"... enough heat generated by the intense pressure that it melts the dust sufficiently to fuse it..."

Are you speaking about powder-metal, or sintered, parts?

I didn't know, and based on those descriptions, not quite either. My only function was to design the bunkers holding the "Iron Dust" but I was told that they did it much like your powder-metal link except that the compaction was from an explosion, and the heat was generated by the pressure from the explosion. This was in 1966, perhaps an early stage in development of the method?

Could be, I am not real familiar with the history of the process.

I have seen a few training films and have a friend in the sintered parts business. The door hardware that I sell relies heavily on sintered parts. Your description (all except the explosive pressure) seemed very similar to what I have seen.

From what I can gather, these sintered parts can be machined, but they don't like to be deformed/swaged at all. With Milo's illustration and description in the OP, that makes perfect sense.